Ras regulates interleukin-1β-induced HIF-1α transcriptional activity in glioblastoma

We observed elevated levels of pro-inflammatory cytokine IL-1 beta in glioblastoma multiforme tumor samples. Since hypoxia-inducible factor-1 alpha (HIF-1 alpha) plays a crucial role in linking inflammatory and oncogenic pathways, we investigated the effect of IL-1 beta on HIF-1 alpha expression in glioma cells under normoxia. IL-1 beta-mediated elevation of HIF-1 alpha transcriptional activity was dependent on Ras-induced NF-kappa B activation, as IL-1 beta failed to induce NF-kappa B and HIF-1 alpha activity in cells transfected with dominant negative RasN17. Increased Ras expression was accompanied by increased phosphorylation of Ras effectors AKT, ERK, INK, and p38MAPK. While inhibition of these effectors individually failed to block the IL-1 beta-mediated increase in HIF-1 alpha induction, co-inhibition of both AKT aid ERK resulted in a significant decrease in IL-1 beta-induced HIF-1 alpha activation. Interestingly, IL-1 beta elevated Wnt-1 expression in a Ras-dependent manner, and small interfering RNA (siRNA)-mediated knockdown of Wnt-1 decreased HIF-1 alpha activity. Although Wnt-1-mediated HIF-1 alpha was independent of the canonical Wnt/beta-catenin signaling pathway, it regulated HIF-1 alpha through NF-kappa B. siRNA-mediated HIF-1 alpha knockdown attenuated elevated IL-1 beta mRNA levels induced upon IL-1 beta treatment. This was accompanied by increased interaction of HIF-1 alpha with H1F responsive element on the IL-1 beta promoter upon IL-1 beta treatment, under normoxia. Our studies highlights for first time that (1) Ras is a key mediator of IL-1 beta-induced NF-kappa B and HIF-1 alpha activation, under normoxia; (2) Wnt-1 regulates IL-1 beta-mediated HIF-1 alpha induction via NF-kappa B; (3) Ras and Wnt-1 are intermediaries in the canonical IL-1 beta-NF-kappa B signaling pathway downstream of MyD88; and (4) IL-1 beta-induced HIF-1 alpha drives a HIF-1 alpha-IL-1 beta autocrine loop to maintain persistently elevated IL-1 beta level.